Fuel burner control system

ABSTRACT

An all solid state control system which is adapted to be connected to a fuel burner is disclosed that uses a pair of solid state switches each having a radiation responsive gating means that is responsive to a single radiation generator means. The first solid state switching means is gated &#39;&#39;&#39;&#39;on&#39;&#39;&#39;&#39; to energize the fuel burner or load, while the second radiation responsive gating means is gated &#39;&#39;&#39;&#39;on&#39;&#39;&#39;&#39; to continuously energize the radiation generator means to act as a latching mechanism to hold the system energized. The radiation generator means is initially energized through a flame responsive circuit and thermostat to initiate operation of the system.

United States Patent Hron Aug. 7, 1973 FUEL BURNER CONTROL SYSTEM Primar Examiner-Edward G. Favors 75 Inventor. Roland L. Hron Bloomm t y 1 Min. g on i t rg r y Lamont B. Koontz and Alfred N. Feldman [73] Assignee: Honeywell lnc., Minneapolis, Minn. [57] ABSTRACT 22 Filed; June 2 972 An all solid state control system which is adapted to be [52] US. Cl. 431/69, 431/79 [51] lnt. Cl. F23n 5/08 [58] Field of Search 431/69, 79

[56] References Cited UNITED STATES PATENTS 3,286,761 11/1966 Engh 431/79 X 3,463,600 8/1969 Axmark 431/16 3,574,496 4/1971 Hewitt 431/79 X connected to a fuel burner is disclosed that uses a pair of solid state switches each having a radiation responsive gating means that is responsive to a single radiation generator means. The first solid state switching means is gated on to energize the fuel burner or load, while the second radiation responsive gating means is gated on to continuously energize the radiation generator means to act as a latching mechanism to hold the system energized. The radiation generator means is initially energized through a flame responsive circuit and thermostat to initiate operation of the system.

10 Claims, 2 Drawing Figures FUEL BURNER CONTROL SYSTEM BACKGROUND OF THE INVENTION Fuel burner control systems have as one of their primary considerations the safe and reliable operation of the burner. In order for this to be accomplished, the control system itself must use reliable components. An earlier system which utilizes generally solid state components is disclosed in the U.S. Pat. No. 3,416,038 to Mierendorf. This circuit utilizes a conventional relay and this relay has been found to be one source of potential trouble. An attempt to avoid this type of relay problem has been approached by substituting solid state devices for the relay as is shown in patents such as the U.S. Pat. No. 3,671,169 to Hron et al. and U.S. Pat. No. 3,672,81 l to Hron. Both of these last cited circuits use solid state components and use a single photo responsive resistor for operation in responseto two light sources. This type of an arrangement lends complexity to the overall system and is avoided by the simplified arrangement of the present invention.

SUMMARY OF THE INVENTION The present invention is directed to a fuel burner control system that is adapted to be connected to a fuel burner means, a condition sensing means or thermostat, and which is capable of reliable operation through the use of solid state components. The multiple switching functions that are normally accomplished by a relay are accomplished in the present invention by the use of a radiation generator means or light that operates a pair of radiation responsive solid state switch means. This pair of switch means acts as, firstly a means of switching on" the load or fuel burner itself, and secondly as a latching means for the device. Components or packages which include a single light source and two photo responsive cells are available, but their application to the particular type of circuit involved was not readily apparent. This circuit requires not only the latching function of the relays, but a safe means of energizing the circuit and reliably sensing the existence or absence of a flame in conjunction with other'safety equipment. The present fuel burner control system is unique in its safe operation and solid state reliability.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 of the present application is a complete schematic diagram of a burner control system adapted to be connected to a load such as a fuel burner, a condition responsive means such as a thermostat, and to a flame responsive device such as a photo or flame responsive resistor, and;

FIG. 2 is a portion of the circuit showing a radiation generator means utilizing a full-wave bridge and light emitting diode.

DESCRIPTION OF THE PREFERRED EMBODIMENT The preferred embodiment includes a fuel burner control system generally disclosed at which is adapted to be connected by way of seven external terminals 11 to 17 .to a load 20 in the form of a fuel burner, a condition responsive means 21 in the form of a thermostat, and a flame responsive resistor means 22 that normally wouldbe a cadmium sulfide cell. The fuel burner control system -10 is also adapted to be connected by terminals 11 and 13 to a conventional source of alternating current supplied between conductors 23 and 24. 1 v i A transformer means25 is disclosed having a primary winding 26 that is connected by conductor 27 to terminal 11 and by conductor 28 and fuse 30 to terminal 13. This provides the necessary energizing potential for the transformer means 25 which in turn energizes a tapped secondary winding 31.

Included in the line or source side of the fuel burner control system 10 is gated solid state switch means 32 in the form of a triac which is connected between the terminal 12 and the conductor 28. A gate 33 is connected through a resistor 34 to conductor 28 and the gate 33 is also connected to a radiation responsive gating means 35 in the form of a light responsive resistor or cadmium sulfide cell. The resistor 34 and the cadmium sulfide cell 35 are connected in series to form a gating circuit for the triac 32.

The tapped secondary winding 31 has a conductor 36 which is connected through a normally closed safety switch contact 37 of a conventional design which mechanically locks in an open position once it is activated. The normally closed safety switch contact 37 is operated in response 'to a safety switch heater means 38 and this is indicated by the dash connection 39. The nor- -mally closed contact 37 is connected b'yco'nductor 40 through a resistor 41 to the terminal "16 and then through the flame responsive resistor means 22 to terminal 17 where it is connected by conductor 42 back to the tapped secondary winding 31. The circuit including the normally closed contact 37 and the flame responsive resistor means 22 forms a flame responsive circuit means that acts as a gating arrangement through a resistor 43, a switch (such as a diac) 44, and a resistor 45. The junction 46 between the bidirectional switch 44 and the resistor 45 is connected to a second gated solid state switch means in the form of a silicon controlled rectifler 50. The silicon controlled rectifier is connected in series with the safety switch heater means 38 and a radiation generator means 51 which is disclosed as a simple incandescent light bulb. The light bulb 51 is connected through a paralleled resistor 52 and diode 53 to a conductor 54 that is in turn connected to the terminal 15 and through the thermostat 21 to the terminal 14. This series circuit is adapted to be energized whenever the thermostat 21 closes, and the resistor 52 has been placed in the circuit to insure that the control will not tum on below a given line voltage level. Diode 53 has been placed in the circuit to adjust current values for proper latching of the silicon controlled rectifier 56. Their presence is not essential, but are disclosed as a practical means of controlling the minimum line voltage at which the control will function.

A tap 55 of the tapped secondary winding 31 is connected through a gated solid state switch means 56 disclosed as a silicon controlled rectifier which is in turn connected by conductor 57 toa junction 58 between the incandescent light 51 and the safety switch heater means 38. The silicon cntrolled rectifier 56 has agate 60 that is connected through a resistor 61 to the conductor 57 and also through a radiation responsive means 62 back to the tap 55 on the tapped secondary winding 31. The radiation responsive means 62 forms a radiation gating means for the silicon controlled rectifier 56 and again can be a cadmium sulfide cell.

The radiation generator means or incadescent light 51 emits a radiation or light indicated at 63 which falls on both of the radiation gating means or cadmium sulfide cells 35 and 62. These three elements, that is the light 51 and the two cells 35 and 62, are enclosed in a light tight package so only the radiation from the radiation generating means 51 falls on the two cells 35 and 62.

To complete the hookup of the present system in a practical matter a resistor 65 is connected between the conductor 57 and the terminal of the thermostat 21 to provide a current conduction, path that is necessary to provide a correct current balance in the thermostat for proper cycling of the thermostat in a conventional manner. The resistor 65 has been added solely for this purpose and is not essential to the operation of the basic burner control system.

DESCRIPTION OF OPERATION OF FIG. 1

It is initially assumed that the load or fuel burner is off but that power is supplied between conductors 23 and 24 thereby energizing the transformer means 25. The thermostat 21 is open and the photo responsive cadmium sulfide cells 22, 35 and 62 are all relatively high in values since they are exposed to dark environments. The flame responsive resistor means 22 is in a dark environment since the fuel burner 20 is off, and cadmium sulfide cells 35 and 62 are in a dark environment since the incandescent light 51 is off.

Upon a call for heat, the thermostat 21 closes thereby completing a circuit through the normally closed switch 37 and the conductor 40 through the resistor 41 and the resistors 43, 45 and the bidirectional switch 44. The application of voltage on this circuit triggers the silicon controlled rectifier. 50 into conduction when conductor 40 is positive with respect to conductor 42. The triggering of the silicon controlled rectifier 50 into conduction allows current to flow through the thermostat 21, the resistor 52, the incandescent light 51, and the safety switch heater means 38. This current flow performs two functions. The first is to energize the incandescent light 51 and secondly provides an energizing voltage to check the continuity of and start the operation of the heating of the safety switch heater means 38. On the reverse half cycle nothing happens since the silicon controlled rectifier can only conduct in one direction. After a short number of half cycles, the current flow through the incandescent light 51 is sufficient to supply radiation to the cadmium sulfide cells 35 and 62 lowering their resistances and thereby gating on" the triac 32 and the silicon controlled rectifier 56.

As soon as the triac 32 begins to conduct due to the lowering of the resistance of the cadmium sulfide cell 35, current flows on both half cycles through the load or oil burner 20. The oil burner 20 starts the conventional flow of fuel and ignition process, and the ignition of the fuel must occur within a preset time or the heating of the safety switch heater means 38 will cause the switch 37 to open and lock out requiring manual reset in a conventional manner.

If it is assumed that flame is generated in the fuel burner 20, this flame will cause the radiation to fall on the cadmium sulfide or flame responsive resistor means 22 thereby lowering its resistance substantially. This effectively shorts out the gate of the silicon controlled rectifier 50 and it ceases to conduct. The energy from the incandescent light 51 has during this period of time been falling on the cadmium sulfide cell 62 causing it to gate thesilicon controlled rectifier 56 into conduction on half cycles thereby reinforcing the current flow through the incandescent light 51 in the reverse direction from that which triggered the system into initial operation. The diode 53 has been provided to allow for a substantial current flow each time the proper half cycle is applied so that the silicon controlled rectifier 56 conducts. The light falling on the dacmium sulfide cell 62 from the source 51 keeps the silicon controlled rectifier 56 in conduction which in turn keeps the light energized. This, in effect, acts as a locking or holding contact of a relay and since the cadmium sulfide cells 35 and 62 have a substantially long memory of the light, that is the resistance of these cells remains relatively low for a period of time after the light has been removed, the system does notde-energize on the half cycles of a reverse polarity to the silicon controlled rectifier 56.

With the arrangement disclosed the system remains in operation as long as the thermostat 21 allows current to flow through the light 51 to keep the cell 62 in a low resistance value. tI-Ie shorting out of the gate circuit of the silicon controlled rectifier 50'bythe lowering of the resistance of the flame responsive resistor means 22 deenergizes the safety switch heater means 38. With the arrangement thus disclosed, a substantially all solid state burner control system has been disclosed and provides a distinct advantage over a conventional electromagnetic relay which has contacts which wear and erode during operation thus limiting the life of the conventional relay operated system.

The incandescent light 51 can be replaced by solid state components as is disclosed in FIG. 2. In FIG. 2 a light emitting diode is disclosed in a full-wave bridge arrangement made up of diodes 71. In series with the legs of the bridge are a pair of resistors 72 and 73. The resistors 72 and 73 have been picked to provide proper current flows through the light emitting diode for controlling the minimum operating voltage level and latching on the two half cycles of the current applied. The resistors 72 and 73 have a common junction 74 which is connected as at terminal 15 of FIG. 1. The diodes at the opposite end of the bridge have a junction 75 that is connected at junction 58. The bridge configuration including the light emitting diode 70 can be substituted for the incandescent light 51 and the resistor 52 along with its parallel diode 53.

The operation of this system including the light emitting diode 70 is identical to that of the system as described in FIG. 1. The current flow between the terminal 15 and the junction 58 is through the light emitting diode 70 which in turn provides the illumination or radiation for the cadmium sulfide cells 35 and 62. With the light emitting diode, it is possible to provide an all solid state configuration. The selection of an incandescent light 51 versus the light emitting diode 70 is a matter of economics and convenience, and thesetwo arrangements are completely interchangeable in the presently disclosed fuel burner control system.

The present invention provides for a solid state burner control system having the unique properties of eliminating all mechanical components except the normally closed safety switch contact 37, which for safety reasons must be a mechanical switch that is capable of being locked in an open position so that the device requires manual reset to bring to the attention of service personnel the fact that some malfunction may have ocqurred in the system. The present invention advances the burner control art by providing more reliable and long lived device and the scope of the present invention is limited solely by the appended claims.

The embodiments of the invention in which an exclusive property or right is claimed are defined as follows: l. A fuel burner control system including: transformer means having a primary winding and a secondary winding with said primary winding adapted to be connected to a source of voltage; gated solid state switch means including radiation responsive gating means for control of said switch means with said switch means adapted to connect a fuel burner to said source; flame responsive circuit means having normally closed safety switch contact means and second gated solid state switch means; said second gated solid state switch means adapted to be connected to flame responsive resistor means; said second gated solid state switch means, safety switch operator means, and radiation generator means forming a series circuit which is adapted to be connected to said secondary winding through said normally closed safety switch contact means by condition responsive means; and third gated solid state switch means including second radiation responsive gating means for control of said third solid state switch means connecting said secondary winding to a junction between said operator means and said radiation generator means; both said radiation gating means being responsive to only the radiation from said radiation generator means. l

2. A fuel burner control system as described .in claim 1 wherein said first solid state switch'means is a triac, said second and third solid state switch means are silicon controlled rectifiers, and said secondary winding has a tap for connection to said third solid state switch means.

3. A fuel burner control system as described in claim 2 wherein both of said radiation responsive gating means are light responsive resistors.

4. A fuel burner control system as described in claim 3 wherein said radiation generator means is an incandescent light.

5. A fuel burner control system as described in claim 4 wherein said series circuit includes a parallel combination of a diode and a resistor to allow said incandescent light to be energized by voltage from said secondary winding on each half cycle of said source by conduction of both of said silicon controlled rectifiers.

6. A fuel burner control system as described in claim 5 wherein a thermostat heater resistor is placed in parallel circuit with said parallel combination of said diode and resistor, and said incandescent light to provide for an adequate current flow in said condition responsive means when said condition responsive means is activated to energize said incandescent light through said last named silicon controlled rectifier.

7. A fuel burner control system as described in claim 6 wherein said safety switch operator means is a resistor, and said operator means is operatively energized during the absence of a flame in said burner to open said normally closed safety switch contact means to de energize and mechanically lock out said flame responsive circuit means and said incandescent light after a pre-selected time to be determined by the heating of said heater means.

8. A fuel burner control system as described in claim '7 wherein said light responsive resistors are both cad- 

1. A fuel burner control system including: transformer means having a primary winding and a secondary winding with said primary winding adapted to be connected to a source of voltage; gated solid state switch means including radiation responsive gating means for control of said switch means with said switch means adapted to connect a fuel burner to said source; flame responsive circuit means having normally closed safety switch contact means and second gated solid state switch means; said second gated solid state switch means adapted to be connected to flame responsive resistor means; said second gated solid state switch means, safety switch operator means, and radiation generator means forming a series circuit which is adapted to be connected to said secondary winding through said normally cLosed safety switch contact means by condition responsive means; and third gated solid state switch means including second radiation responsive gating means for control of said third solid state switch means connecting said secondary winding to a junction between said operator means and said radiation generator means; both said radiation gating means being responsive to only the radiation from said radiation generator means.
 2. A fuel burner control system as described in claim 1 wherein said first solid state switch means is a triac, said second and third solid state switch means are silicon controlled rectifiers, and said secondary winding has a tap for connection to said third solid state switch means.
 3. A fuel burner control system as described in claim 2 wherein both of said radiation responsive gating means are light responsive resistors.
 4. A fuel burner control system as described in claim 3 wherein said radiation generator means is an incandescent light.
 5. A fuel burner control system as described in claim 4 wherein said series circuit includes a parallel combination of a diode and a resistor to allow said incandescent light to be energized by voltage from said secondary winding on each half cycle of said source by conduction of both of said silicon controlled rectifiers.
 6. A fuel burner control system as described in claim 5 wherein a thermostat heater resistor is placed in parallel circuit with said parallel combination of said diode and resistor, and said incandescent light to provide for an adequate current flow in said condition responsive means when said condition responsive means is activated to energize said incandescent light through said last named silicon controlled rectifier.
 7. A fuel burner control system as described in claim 6 wherein said safety switch operator means is a resistor, and said operator means is operatively energized during the absence of a flame in said burner to open said normally closed safety switch contact means to de-energize and mechanically lock out said flame responsive circuit means and said incandescent light after a pre-selected time to be determined by the heating of said heater means.
 8. A fuel burner control system as described in claim 7 wherein said light responsive resistors are both cadmium sulfide cells having relatively long memories of the light incident thereon.
 9. A fuel burner control system as described in claim 1 wherein said radiation generator means includes light emitting diode means.
 10. A fuel burner control system as described in claim 1 wherein said radiation generator means includes a full-wave rectifier bridge and a light emitting diode. 